OBJECTIVE: To assess the 10-year cumulative survival outcome of polymyositis (PM) and dermatomyositis (DM) as well as the factors associated with the the outcome. METHODS: Eighty five patients with PM and twenty one patients with DM were diagnosed at our university medical center between 1997 and 2007. Thirty six patients with PM and 13 patients with DM were followed up until death or until the end of January, 2008. Gender, age, AST, ALT, CPK, LDH, ESR, CRP, aldolase, drugs of therapy, combined ILD, and cancer, and duration of remission after therapy were assessed as prognostic factors of death by the Kaplan-Meier curve and Cox regression model. RESULTS: The respective 10-year survival rate for PM and DM was 80.8% (95% confidence interval (CI): 73.3~87.2) and 55.9% (95% CI: 40.7~71.1), respectively. The median survival for PM and DM was 11.3 years (95% CI: 9.8~12.9) and 7.0 years (95% CI: 3.6~10.5), respectively. Compared to DM patients, the subjects with PM had a 167.26 fold (95% CI: 7.59~3683.19) combined ILD adjusted risk of mortality (p<0.05) and no other individual factor reached significance as a predictor of death. However, cancer had a hazard ratio (HR) of 17.00 (95% CI: 1.06~281.79) and 2.45 (95% CI: 0.78~12.45) for death in the PM and DM group, respectively. CONCLUSION: According to an analysis of the survival and its prognostic factors in patients with PM and DM, ILD is a risk factor for mortality in PM and cancer was risk factor for mortality in both PM and DM.